Impact of Debris-flow sediments on the Longitudinal Profile along Min River in the Wenchuan Earthquake Region

Abstract:

The Wenchuan earthquake induced large number of sediments from landslides, and subsequent sediment-related hazards such as debris flows constricting or blocking the streamflow changed the river longitudinal profile. Twenty-seven debris-flow sediments that directly blocking the river were identified via remote-sensing interpretation and field survey, distributing along the Min river from Wenchuan to Yingxiu segment. A methodology combining the stream-power incision model and ALOS-2 (PALSAR-2) DEM with resolution of 12.5 m×12.5 m is used to analyze the geomorphic effect of debris-flow sediments on Min River. According to superimpose river longitudinal profile, debris-flow sediments distribution, faults, lithologic, and the location of hydroelectric power station on the log elevation-distance plots, the influence of various factors on river longitudinal profile morphology was analyzed. The results show that the repeated debris-flow sediments, which transported into Min river during 2008 to 2013 raised the upstream of Min riverbed, while eroding the river bed at the knickpoints. Two peak values of river steepness index (k_sn) and slope could not be explained by lithologic contacts, or rock uplift on faults, indicates that debris flow sediments have a good spatial correlation with river knickpoint, which provides insights into the significantly role of mass wasting processes in river morphology and long-term valley evolution.